1. Field of the Invention
This invention relates to a customized passive hearing protection earplug and to a method for manufacturing the same.
2. Description of Related Art
A large part of the population is exposed to hazardous noise from time to time. This can be at work, whilst traveling, during leisure activities or at home. The exposure can lead to permanent hearing loss, distract people's attention from other hazards or simply cause stress. In order to prevent both accidents and permanent hearing damage, hearing protection devices (HPDs) have been provided in many styles and over many years. It started with the earmuff which is still very relevant and addresses very noisy environments (e.g. airports, construction, shooting) or complex working/communication situations (e.g. fighter pilots). Over the years development of biocompatible soft materials has enabled soft earplugs in different styles and colors as well as recent development of “one fits many” standard semi-soft earplugs in silicon-rubber type materials. For severe situations even the combination of an earmuff and an “in-the-ear” HPD is required to achieve desired attenuation. The physical limitation of hearing protection based on ear worn devices is defined where bone-conduction (body acoustics) becomes dominant at around 40 dB attenuation.
A common disadvantage of the above mentioned HPD styles is wearing discomfort. In case of the earmuffs, they are large which creates difficulties in combination with other head worn gear and they “close off” the ear too much for most applications. The in-the-ear styles mentioned are devices made to fit “the average” ear in one way or the other. Either the fit is provided by softness of the material which leads to undefined device insertion and undefined attenuation, or the fit is provided by standard shaped structures intended to block off the ear canal. In both cases the flat distribution of the individual shape of the outer ear and the ear canal leads to bad fit, pressure points in the ear and undefined positioning of the device.
To address this wearing comfort issue, in-the-ear hearing aid technology has been applied making customized ear molds with passive acoustical filter. These are long lasting devices with good wearing comfort. However, this customization process is traditionally a very manual process creating varying results over time, low reproducibility and the quality is very operator skill dependent.
The idea to use rapid prototyping technology, such as layer-by-layer laser sintering, in manufacturing shells, primarily for hearing aids, is described, for example, in U.S. Pat. No. 6,533,062 B1 or US 2003/0133583 A1.
HPDs are often passive (i.e. not powered) and some simply amount to a plug in the ear; while more sophisticated (but still passive) HPDs may include acoustic chambers and filters, for passing or attenuating selected frequencies.
Different in-ear devices are presently used in a wide range of human activities. From the performance standpoint, in particular with respect to comfort, HPDs, like hearing aids, really have to be custom-fitted to an individual's ear shape. In-ear devices are inserted into the outer part of an individual's ear canal and, depending on the size of the in-ear device, may as well occupy parts of an individual's concha, also called pinna.
Often, in-ear HPDs or earplugs of some standard size and a certain damping characteristic are used to cover hearing protection needs of a wide variety of different ear anatomies. For a certain individual, a prediction of the performance of such an earplug is difficult and it is not possible to adapt the earplug's filter characteristic to specific needs of an individual. However, in many cases customized passive HPDs that provide a predictable attenuation of acoustic energies across the audible frequency range are desired. With conventional shell making technology, this has been prepared in form of a more or less sophisticated filter module component. This component is mounted in or on the shell faceplate and provides a defined acoustic “gate” through the HPD. Supply of such filters is rather limited, prices are high and the flexibility in application is not convincing.
U.S. Pat. No. 6,148,821 discloses a selective non-linear attenuating soft earplug which is a passive in-the-ear (ITE) device. A filter tube is inserted into the shell, and the hollow interior of the filter tube may be set into communication with the surroundings by rotating it. A sound attenuating filter is inserted into the distal end portion of the tube. When the filter whose attenuating characteristics cannot be modified, is to be changed against another filter, the tube must be removed from the earplug, and the filter must be replaced. The tube is then to be reinserted into its receiving cavity of the HPD.
Another type of filter is described in the published U.S. patent application no. 2003/0112990; this document is directed to an expandable in-ear device. The filter may be a band-pass filter; it has the shape of a little rectangular block to be inserted into a square-sectioned opening of the earplug from which it slightly protrudes to the exterior. The filter is removably locked to a handle of the HPD that is in turn secured, preferably glued, to the earplug platform. Thus, the filter can normally not be removed from the HPD.
Customized earplugs having a shell with an outer shape corresponding individually to the measured inner shape of the user's outer ear and ear canal which are produced e.g. by layer-by-layer laser sintering from a powder material are described for example in U.S. Pat. No. 6,533,062 B1.
The increasing demand for fully customized HPDs will require flexible devices that are individually fitted regarding both the anatomy and the acoustics of the wearer's ear. For evident reasons, short delivery times and low costs will be determining for a widespread use of new HPDs.
Known prefabricated filter assemblies as such described above are either complicated to handle or, although allowing short delivery, remain expensive.
It is an object of the present invention to provide for a customized hearing protection earplug which allows for an individual and flexible sound attenuation function and which is easy to manufacture. It is a further object to provide for a corresponding manufacturing method.